Colour behaviour of the blazar PKS 0735+178 in 1994–2004 L. O. Takalo, V. A. Hagen-Thorn, E. I. Hagen-Thorn, S. Ciprini and A. Sillanpää A&A, 517 (2010) A63 Published online: 06 August 2010 DOI: 10.1051/0004-6361/200913497